Trichinellosis Causes, Symptoms and Treatment

Trichinellosis is a zoonotic disease caused by Trichinella parasites. The disease occurs worldwide.

Many animals may act as reservoirs, but those most frequently involved in cases of human infection are pigs and horses. In Europe, wild boars have also been implicated.

Infested animals harbour larvae encysted in their muscles, and consumption of raw or undercooked meat products may lead to disease.

Typically, after an incubation phase of about 24–48 hours, fever and intestinal symptoms may appear, due to larvae invading the intestine.

Then, about a week after infection, larval invasion of the muscles begins: muscle aches and fever are characteristic.

Finally, acute symptoms fade, but muscle problems may take a long time to resolve. Depending on the number of viable larvae consumed, symptoms will vary from without any symptoms to extremely severe or even fatal (massive invasion of the bowel and/or massive invasion of internal organs) disease.

Effective treatment is available.

Trichinellosis prevention is based on accurate inspection of all slaughtered pigs and horses, which is mandatory in the EU. Imported and wild animal meat presents a higher risk and its consumption in the undercooked or raw state should be discouraged.

What are the signs and symptoms of a trichinellosis infection?

The signs, symptoms, severity and duration of trichinellosis vary. Nausea, diarrhea, vomiting, fatigue, fever, and abdominal discomfort are often the first symptoms of trichinellosis.

Headaches, fevers, chills, cough, swelling of the face and eyes, aching joints and muscle pains, itchy skin, diarrhea, or constipation may follow the first symptoms.

If the infection is heavy, patients may experience difficulty coordinating movements, and have heart and breathing problems. In severe cases, death can occur.

For mild to moderate infections, most symptoms subside within a few months. Fatigue, weakness, muscle pain, and diarrhea may last for months.

How soon after infection will symptoms appear?

Abdominal symptoms can occur 1-2 days after infection. Further symptoms usually start 2-8 weeks after eating contaminated meat.

Symptoms may range from very mild to severe and relate to the number of infectious worms consumed in meat.

Often, mild cases of trichinellosis are never specifically diagnosed and are assumed to be the flu or other common illnesses.

How does infection occur in humans and animals?

When a human or animal eats meat that contains infective Trichinella cysts, the acid in the stomach dissolves the hard covering of the cyst and releases the worms.

The worms pass into the small intestine and, in 1-2 days, become mature.

After mating, adult females lay eggs. Eggs develop into immature worms, travel through the arteries, and are transported to muscles.

Within the muscles, the worms curl into a ball and encyst (become enclosed in a capsule).

The life cycle repeats when meat containing these encysted worms is consumed by another human or animal.

Am I at risk for trichinellosis?

If you eat raw or undercooked meats, particularly bear, pork, wild feline (such as a cougar), fox, dog, wolf, horse, seal, or walrus, you are at risk for trichinellosis.

Can I spread trichinellosis to others?

What should I do if I think I have trichinellosis?

See your health care provider who can order tests and treat symptoms of trichinellosis infection. If you have eaten raw or undercooked meat, you should tell your health care provider.

How is trichinellosis infection diagnosed?

A blood test or muscle biopsy can show if you have trichinellosis.

How is trichinellosis infection treated?

Several safe and effective prescription drugs are available to treat trichinellosis.

Treatment should begin as soon as possible and the decision to treat is based upon symptoms, exposure to raw or undercooked meat, and laboratory test results.

How can I prevent trichinellosis?

The best way to prevent trichinellosis is to cook meat to safe temperatures. A food thermometer should be used to measure the internal temperature of cooked meat. Do not sample meat until it is cooked. USDA recommends the following for meat preparation.

For Whole Cuts of Meat (excluding poultry and wild game)

Cook to at least 145° F (63° C) as measured with a food thermometer placed in the thickest part of the meat, then allow the meat to rest* for three minutes before carving or consuming.

For Ground Meat (excluding poultry and wild game)

Cook to at least 160° F (71° C); ground meats do not require a rest* time.

For Wild Game (whole cuts and ground)

Cook to at least 160° F (71° C).

For All Poultry (whole cuts and ground)

Cook to at least 165° F (74° C), and for whole poultry allow the meat to rest* for three minutes before carving or consuming.

*According to USDA, “A ‘rest time’ is the amount of time the product remains at the final temperature, after it has been removed from a grill, oven, or other heat source.

During the three minutes after meat is removed from the heat source, its temperature remains constant or continues to rise, which destroys pathogens.”

Curing (salting), drying, smoking, or microwaving meat alone does not consistently kill infective worms; homemade jerky and sausage were the cause of many cases of trichinellosis reported to CDC in recent years.

Freeze pork less than 6 inches thick for 20 days at 5°F (-15°C) to kill any worms.

Freezing wild game meats, unlike freezing pork products, may not effectively kill all worms because some worm species that infect wild game animals are freeze-resistant.

Clean meat grinders thoroughly after each use.

To help prevent Trichinella infection in animal populations, do not allow pigs or wild animals to eat uncooked meat, scraps, or carcasses of any animals, including rats, which may be infected with Trichinella.